/*

 * Licensed to the Apache Software Foundation (ASF) under one

 * or more contributor license agreements.  See the NOTICE file

 * distributed with this work for additional information

 * regarding copyright ownership.  The ASF licenses this file

 * to you under the Apache License, Version 2.0 (the

 * "License"); you may not use this file except in compliance

 * with the License.  You may obtain a copy of the License at

 *

 *     http://www.apache.org/licenses/LICENSE-2.0

 *

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

 * limitations under the License.

 */

package com.bff.gaia.unified.sdk.extensions.euphoria.core.translate;



import com.bff.gaia.unified.sdk.extensions.euphoria.core.client.functional.UnaryFunction;

import com.bff.gaia.unified.sdk.transforms.DoFn;

import com.bff.gaia.unified.sdk.transforms.PTransform;

import com.bff.gaia.unified.sdk.transforms.ParDo;

import com.bff.gaia.unified.sdk.values.KV;

import com.bff.gaia.unified.sdk.values.PCollection;

import com.bff.gaia.unified.sdk.values.TypeDescriptors;



import javax.annotation.Nullable;



/**

 * A transform for extracting stamp and applying a user-defined transform on the extracted

 * collection.

 *

 * @param <InputT> input type

 * @param <OutputT> output type

 */

public class TimestampExtractTransform<InputT, OutputT>

    extends PTransform<PCollection<InputT>, PCollection<OutputT>> {



  /**

   * Create transformation working on KVs with timestamps as key.

   *

   * @param <InputT> type of input elements

   * @param <OutputT> type of output elements

   * @param transform the transform applied on elements with timestamp

   * @return the transform

   */

  public static <InputT, OutputT> TimestampExtractTransform<InputT, OutputT> of(

      PCollectionTransform<InputT, OutputT> transform) {



    return new TimestampExtractTransform<>(null, transform);

  }



  /**

   * Create transformation working on KVs with timestamps as key.

   *

   * @param <InputT> type of input elements

   * @param <OutputT> type of output elements

   * @param name name of the transform

   * @param transform the transform applied on elements with timestamp

   * @return the transform

   */

  public static <InputT, OutputT> TimestampExtractTransform<InputT, OutputT> of(

      String name, PCollectionTransform<InputT, OutputT> transform) {



    return new TimestampExtractTransform<>(name, transform);

  }



  /**

   * Apply user defined transform(s) to input {@link PCollection} and return output one.

   *

   * @param <InputT> input type

   * @param <OutputT> output type

   */

  @FunctionalInterface

  public interface PCollectionTransform<InputT, OutputT>

      extends UnaryFunction<PCollection<KV<Long, InputT>>, PCollection<OutputT>> {}



  private static class Wrap<T> extends DoFn<T, KV<Long, T>> {



    @ProcessElement

    public void processElement(ProcessContext ctx) {

      ctx.output(KV.of(ctx.timestamp().getMillis(), ctx.element()));

    }

  }



  private static class Unwrap<T> extends DoFn<KV<Long, T>, T> {



    @ProcessElement

    public void processElement(ProcessContext ctx) {

      ctx.output(ctx.element().getValue());

    }

  }



  private final PCollectionTransform<InputT, OutputT> timestampedTransform;



  private TimestampExtractTransform(

      @Nullable String name, PCollectionTransform<InputT, OutputT> timestampedTransform) {



    super(name);

    this.timestampedTransform = timestampedTransform;

  }



  @Override

  public PCollection<OutputT> expand(PCollection<InputT> input) {

    PCollection<KV<Long, InputT>> in;

    in = input.apply(getName("wrap"), ParDo.of(new Wrap<>()));

    if (input.getTypeDescriptor() != null) {

      in =

          in.setTypeDescriptor(

              TypeDescriptors.kvs(TypeDescriptors.longs(), input.getTypeDescriptor()));

    }

    return timestampedTransform.apply(in);

  }



  private String getName(String suffix) {

    return name != null ? name + "::" + suffix : suffix;

  }

}